No abstract

Lupus anticoagulant is associated with thrombosis and pregnancy morbidity, and its detection is of major clinical importance. The nature and concentration of phospholipids strongly influence the sensitivity of activated partial thromboplastin time (aPTT) reagents to lupus anticoagulant. We investigated the ability of Platelin LS, an aPTT reagent, to screen lupus anticoagulant among 94 patients with venous thromboembolism by comparing its performance with the dilute Russell viper venom time (dRVVT). Twenty-four patients had an abnormal aPTT and dRVVT, whereas 37 only had a prolonged dRVVT. In users of oral anticoagulants (n = 56), the dRVVT prolonged more frequently than the aPTT (98.2 vs 39.3%, P < 0.0001). After the mixing study, seven patients maintained abnormal aPTT and dRVVT ratios, five of whom had prolonged mixture with both tests. The agreement in the mixing study between aPTT and dRVVT was substantial (kappa = 0.78, 95% confidence interval = 0.48-1.00). Except for one patient, the aPTT screened all cases that demonstrated phospholipid dependency of their inhibitor during the confirmatory procedure with the dRVVT. In conclusion, the aPTT using Platelin LS was highly associated with the presence of lupus anticoagulant detected by the dRVVT among patients with venous thromboembolism, and could be reliably employed as a screening assay for lupus anticoagulant.

INTRODUCTION: To rule out the presence of LA antibodies, two or more assays that are sensitive to these antibodies must be negative. The dilute Russell’s Viper Venom Time (dRVVT) and the activated partial thromboplastin time (aPTT) using sensitive reagents have been employed to detect LA. The aim of this study was to assess the concordance level of aPTT using Platelin LS and dRVVT as screening tests to identify LA in patients with venous thromboembolism (VTE). METHODS: 94 patients (58 women, 62%) with VTE were evaluated. The detection of circulating inhibitor with Platelin LS and dRVVT was based on a prolonged clotting time and a prolonged 1:1 mixture of sample plasma and normal pooled plasma. The confirmation of the phospholipid dependency was performed only with dRVVT. RESULTS: Among the 94 patients, an abnormal test was found in 24 patients (26%) with aPTT and in 61 patients (65%) using dRVVT. After mixing tests, aPTT ratio remained long in 25% of patients with abnormal aPTT, and in 9.8% with long dRVVT. Five patients had a prolonged mixing study identified by both tests, which resulted in a substantial agreement between the two tests (Kappa= 0.78). Confirmatory tests for LA were positive in 5 out of the 6 patients with long dRVVT mixture, resulting in a prevalence of LA detected by dRVVT of 5.3%. The 5 patients with LA detected by dRVVT also had prolonged mixture with aPTT. CONCLUSION: Our results indicate that aPTT with Platelin LS is highly associated with the presence of LA detected by dRVVT and may be suitable as a screening test for LA in patients with VTE.